44 ELEMENTS OF MAMMALIAN ANATOMY. 
intervertebral foramen for the exit of a spinal nerve; (6) 
the articular processes, two of which project craniad and 
PLAN OF A VER- 
TEBRA. 
sp, Spinous process; ar, 
articular process; 7s, 
transverse process; 1c, 
neural canal; pd, pedi- 
cle; dm, lamina; cn, 
centrum or body. 
Fic. 22. 
with the occipital condyles (Fig. 17) of the skull. 
vertebra. 
The former are called the anterior 
articular processes and the latter 
posterior articular processes. 
The first cervical vertebra, or 
atlas, is characterized by its large 
expanded 
processes, the absence of a spinous 
process, and its rudimentary body. 
Its true body in the embryo becomes 
united to the axis as the odontoid 
process. The cranial margin of the 
neural arch is prolonged at each 
side into a process or articulation 
The 
two caudad from each 
horizontally transverse 
root of this articular process is pierced by a foramen giving 
passage to the first spinal nerve 
and the vertebral artery and vein 
(Fig. 23, fr). From the lateral 
opening of this foramen (fr) a 
continued ventrad to 
the middle of the transverse proc- 
ess, where it leads into the trans- 
verse foramen common to the 
The 
vertebral artery and vein course 
through this canal (Fig. 23). 
The axis, or second vertebra, 
is characterized by its odontoid 
process, which projects within the 
groove 1s 
first six cervical vertebre. 
Fic. 23. DorsocaupaL As- 
PECT OF ATLAS. 
tr, Transverse process; nc, 
neural canal; sp, spinous 
process; fi, aperture of 
the transverse foramen 
which enters the atlas at 
vf; asg, anterior artic- 
ular process; sg, poster- 
ior articular process. 
atlas, and also by its elongated spinous process, which pro- 
jects both craniad and caudad. 
The transverse process pro- 
